Interpretive Summary: Many visible traits are the outcome of a biosynthetic pathway. There are two types of genes that are involved in the expression of a biosynthetic pathway. The structural genes encode the information to create the enzymes that are responsible for each step in the pathway. The regulatory genes are responsible for controlling the expression of the structural genes. The structural genes need to be turned-on in the right place at the right time. We have developed a model system using a petunia mutant to study how regulatory genes control the expression of structural genes for the anthocyanin biosynthetic pathway. The anthocyanins are the pigments responsible for flower color.

Technical Abstract:
Differences in structural gene expression are responsible for a wide range of responses from human cancer to patterned flowers. Gene silencing is one of the ways in which gene expression is controlled. We have developed a model system to study anthocyanin gene silencing using a mutation in Petunia (Star mutation) and the ability of certain viruses to reverse the gene silencing mutation. In healthy plants, the star pattern was enhanced (increase in level of gene silencing) under high temperature or light growing conditions. Virus-infection did not significantly influence the star pattern when plants were grown under either low light or low temperature conditions. Under high light and temperature conditions, virus infection reverses silencing leading to a change in the star pattern. These changes in the star pattern corresponded to changes in gene expression. Viral infection had a greater affect on regulatory gene (Wd40, Myc and Myb) expression than on structural gene expression (Chs and Ans).